Image data, in particular medical image data, may be generated by a number of types of image recording devices, e.g. by computer tomographs, X-ray devices or ultrasound devices. They may be used in medical diagnosis, in material examinations or in material sciences. Image data of this type are increasingly being electronically processed and stored.
Moreover, metadata, such as items of information on the identity of an examined person or an examined object, diagnostic or analytical findings with respect to the images or further commentarial information items, are often added to the data to be stored. The metadata may be present in the form of text or numbers. They may be added either automatically or by a user.
Image data and metadata, once they have been stored, can be post-processed at any time after the first, original storage and be stored anew. In the context of instances of post-processing, it is possible, on the one hand, to amplify or clarify constituent parts of an image. Further, it is possible, on the other hand, to alter or erase constituent parts of an image.
The same, in principle, applies to the metadata, the information content of which can be both supplemented and revised after it has been generated for the first time. Overall, the stored information can thus be revised either in a loss-less manner or in a lossy manner, wherein some information is lost. The lossy revision of information is to be regarded as critical, principally when the recovery of the original information is either impossible or possible only by a reexamination of the person or of the object by an examination device that is possibly not free of side effects or not nondestructive.
However, data losses are not desirable with regard to other items of information as well. A main concern in the storage of medical or analytical image data must therefore lie in ensuring that data, once they have been obtained, are retained in a lossless manner. Furthermore, a patient or examination history can be obtained through the lossless retention of information recorded in chronological succession.
Conventional methods for preventing original, lossless data from being erased or overwritten are based on a so-called archive bit being added to the files which contain these data. The term archive bit refers to an identification which identifies the data as archive data which are intended to be stored permanently as such, but without the possibility for alterations. A further conventional possibility includes adding to the data, as they are being used, an identification as “processed” or, “unprocessed”. However, this identification merely gives information about whether an alteration of whatever kind has been made to the data, but without taking account of the type and extent of the alteration. By way of example, changing the contrast or the brightness of image data, which would not alter the actual information content thereof, would already lead to such data being identified as altered.
A data management system which has to ensure that original data are retained in a lossless manner could operate on the basis of conventional data identifications only in such a way that it would store in each case separately all the data identified as archive data or as “processed”. As a result, although the lossless retention of original data would be ensured, a multiplicity of data which have merely been subjected to unimportant changes would also likewise be additionally stored and retained.
This multiplicity of data records stored more or less unnecessarily would on the one hand generate an unnecessarily high storage space requirement, which would rapidly assume untenably large dimensions, particularly in the case of extensive image data. On the other hand, the user who is supposed to work with these data would be overloaded with a flood of insignificant information, which would make practical utilization of the databases and the evaluation of the data history considerably more difficult and virtually impossible for everyday use. In a similar manner to that for image data, this would also apply to text information in the metadata, in which case the storage space requirement is quite generally to be regarded as noncritical.
A data management system which is intended to ensure the lossless retention of all information would be compelled to separately store every revised version of a findings or analysis text. Thus, it would be necessary for example also to store text versions in which all that has been changed is the text format and typeface, but not the information content. For the user, who wishes primarily to utilize the information content, it would be unnecessarily complicated and confusing to have to check different versions of the text in respect of whether merely structural alterations or else alterations to the content have been made.
Finding differences can be complicated and difficult enough even when using different versions of data having altered contents, whether they be image data or text data. Although it is known for text changes and commentaries to be emphasized e.g. by color highlighting, the emphases do not distinguish between changes to contents and structural changes; moreover, the history of the text information across a number of versions cannot be represented in user-friendly fashion. In such a system, it would be left to the user to store only new versions having revised contents as new data records, in order to prevent the creation of a multiplicity of text versions which have matching contents and have only been altered editorially. It would likewise be left to the user to mark changes to contents in such a way that the history of a multiply revised text remains readily understandable and comprehensible for subsequent consideration.
The above-described problems of the lossless retention of original image data and metadata, the storage of such data with a comprehensible processing history and the restriction to a tenable storage space requirement occur particularly with medical diagnosis image data. In this case, image data which reproduce the status of a patient at a specific point in time are obtained by means of imaging methods. Depending on the imaging method, the image data have a high resolution and are very extensive and therefore require an extremely large amount of storage space. The repeated recording of such image data is quite generally not possible at arbitrary later points in time owing to the continual alteration of the patient status.
The image data from imaging methods are supplemented by metadata, which may contain, usually in the form of text statements on the patient's subjective wellbeing, medial findings or the supplementary information on the illness history. In the same way as the image data, the medically relevant metadata cannot readily be reconstructed later, since both the patient's subjective perception and the patient's illness history change with time. Moreover, a medical point of view that has changed with time may lead to different findings.
Furthermore, it is necessary precisely in the case of medical data to enable an assessment at later points in time or by other medical experts, e.g. in the context of the medical documentation obligation or in the case of use in a knowledge-based system. This presupposes the retention of lossless original data in the case of different instances of processing in the same way as a tenably low storage outlay for the purpose of sufficiently rapid processing and also a representation of the temporal evolution of the data which is comprehensible in a user-friendly manner.